Temperature differential to blame for bridge problems

Temperature differential to blame for bridge problems

(June 19, 2015) When you mix a lot of hot air with loads of cool water, you don’t just get a recipe for fixing Congress, sometimes you get a stuck bridge too.

The Town of Ocean city reported via its Twitter account on Tuesday morning that the Harry Kelley drawbridge was stuck in the “up” position, and that the problem had been resolved a few minutes later. While the phenomenon was not new, it was a novel incident in Ocean City in one respect.

“When the bridge tender closes the drawbridge it has to seat properly — a sensor has to say it’s OK,” David Buck of the State Highway Administration said, “What we’ve never seen in Ocean City is the significant difference between the air and water temperatures affecting the sensor.”

The sensor is attached to a metal spring that must compress to a certain degree for the sensor to show the bridge is seated properly for safe travel. The warmer air, measuring almost 80 degrees near the time of the incident by www.wunderground.com, caused the metal spring to expand; the cooler water, measured at about 67 degrees around the same time by NOAA, was enough to play havoc with the sensor’s tolerances. The bridge, which may have been seated properly, was still showing the bridge was in the “up” position.

The fix is somewhat underwhelming.

“We just had to reopen and reclose the bridge,” Buck said, “The operator let off the button too early. If it was held down for a couple of seconds longer it would have seated properly.”

Buck said the incident was a “little bit of operator error and a little bit miscalibrated sensor.”

A potentially more exciting fix Buck suggested would be to “get out there with a fire hose and cool everything down,” but instead the State Highway Administration said it would send someone out on Wednesday to adjust the sensor.

“We know what it is because we’ve seen it on other bridges,” Buck said, “We just need to convince the sensor the difference is much less than what it is.”

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